Sealed combustion gas-fired infrared heater

ABSTRACT

A gas fired infrared heater is provided that includes a burner, a combustion chamber, a cooling air passage for supplying cooling air to the combustion chamber, a combustion air passage for supplying combustion air to the burner; and an outlet passage allowing combustion product gases to exit the combustion chamber. The cooling air passage is separate from the combustion air passage. The cooling air passage and the combustion air passage both draw from the same pressure zone into which combustion products exit.

FIELD OF THE INVENTION

The present invention relates to a gas-fired infrared heating apparatus;particularly a heating apparatus that completely segregates an incomingcombustion air flow from an incoming radiation-transmissive panelcooling air flow, both of which draw from the pressure zone to whichcombustion products exit, and that segregates both from the combustionchamber itself.

BACKGROUND OF THE INVENTION

A heating device having a fuel-fired radiant burner has long been usedfor heating various enclosures. The heating device here describedincludes a thin, radiation-transmissive panel that transmits infraredradiation into the space to be heated (e.g., room, tent) and also sealsa combustion chamber which houses a radiant from the space being heated.To maintain the integrity of the heating device, the panel must becooled.

One way to cool the panel is to have a stream of cooling air flow (e.g.,by convection) over the panel. An additional way to cool the panel is toprovide a coolant outside the combustion chamber. Another way to coolthe panel is to use suction generated when combustion air is entrainedby gas jets in infrared-generating burners. However, one problem withthis approach is that turbulence in the flame area creates enoughadmixture of combustion products with incoming combustion air tointerfere with clean combustion (e.g., these units produced too muchcarbon monoxide from recirculation.) Another problem with this approachis that back drafts can cause impaired combustion, carbon monoxideformation, or snuffing of the flame.

Accordingly, there is a need for a heating device that satisfies thefollowing conditions, specifically an apparatus that seals off acombustion chamber from the space to be heated and prevents air in thecombustion chamber from being used for combustion.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a heating apparatusthat seals off a combustion chamber from a heated space and supplies allcombustion air to the burner with no possibility of admixture withcombustion chamber gases.

One aspect of the present invention includes a burner, a combustionchamber, a cooling air passage for supplying cooling air to thecombustion chamber, a combustion air passage for supplying combustionair to the burner, and an outlet passage allowing combustion productgases to exit the combustion chamber. In this apparatus, the cooling airis separate from the entering combustion air.

Thus, according to the present invention, it is possible for the heatingapparatus to draw cooling air in without using gas-jet entrainment ofthe burner by, in part, entraining considerable air as hot products moveupward through the outlet passage.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will be described withreference to the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a heater of the invention;

FIG. 2 is a cross-sectional view of a second embodiment of theinvention;

FIG. 3 is a cross-sectional view of a third embodiment of the invention;

FIG. 4 is a cross-sectional view of a forth embodiment of the invention;

FIG. 5 is a cross-sectional view of a fifth embodiment of the invention;

FIG. 6 is a cross-sectional view of a sixth embodiment of the invention;

FIG. 6 b is a planar view of the sixth embodiment of the invention; and

FIG. 7 is a cross-sectional view of a seventh embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described hereinafter withreference to the accompanying drawings.

Referring to FIG. 1, the heater of the invention is designated by areference numeral 2, and as shown in an exemplary position as beingsecured to a ceiling 4 of an enclosure to be heated (e.g., tent,bathroom, ice-fishing shanty, mobile home, etc.) A combustion chamber 6is provided with generally upright side walls 8, 10, a front and rearwall (not shown) and a bottom wall 12, with a radiation-transmissiveport therein. The port may extend between the side walls 8, 10 and thefront and rear walls of the combustion chamber 6, although it may bedesirable, in some instances, to have a smaller port. A sealing barrier14 is located to close the port, and may be fastened by clamps, splinein groove, or the like (not shown) to the periphery of the front, rear,and side walls of the combustion chamber 6.

The sealing barrier 14 is desirably of a thin, flexible plastic materialwhich ordinarily softens or melts below 1000° F. Preferred materials forthe panel include such thermoplastics as polytetrafluoroethylene (Teflon“TFE”, a trademarked product of E. I. DuPont DeNemours and Company,Inc.) which has an infrared transmissivity of approximately 0.88, poly(tetrafluoroethylene-hexafluoropropylene) (Teflon “FEP”, manufactured bythe DuPont Company) which has an infrared transmissivity of 0.97, andpolyester materials such as poly (ethyleneterephthalate) a product soldunder the name Mylar by the DuPont Company and which has an infraredtransmissivity of approximately 0.77. Teflon FEP film having a thicknessof approximately 0.002 inches is preferred, since this material isflexible, is highly transmissive of infrared radiation, and is moreresistant to high temperatures than many other polymeric materials.

Combustion product gases from a burner 16 which are propelled downwardlytoward the sealing barrier 14 are typically hotter than the continuouslyreplenished pool of cooling air (described below), and mix with theupper portion of the latter and rise toward the outlet port 26 beforeimpinging on and damaging the sealing barrier 14.

The sealing barrier 14 is protected from such high temperatures thatresult from hot gases produced by combustion by cooling air 48 drawninto the chamber 6 in such a way that it pools (in this configuration)or sweeps adjacent to the sealing barrier 14. Teflon, sealing barrier14, tends to elongate slightly when heated. Cooling air 48 (describedbelow) keeps it below the melting point, but the sealing barrier 14 mayabsorb enough infrared to warm up and elongate. The reduced pressure inthe combustion chamber 6 (created by the stack action, described below,which pulls cooling air through the cooling chamber) could draw theelongated portion toward a combustion-heated area, nearer to a burner16, such as an ainfrared producing ceramic-faced gas burner. Therefore,to prevent the sealing barrier 14 from melting, one or more fineinfrared-reflective wire(s) 42 are provided along an inner surface ofthe sealing barrier 14.

Located within the combustion chamber 6 is the burner 16. The rearwardend of the burner 16 includes a combustion air inlet 18 connected to acontrol valve 20 that is located outside the combustion chamber 6 andconnected to a downstream gas supply 22. While it can be seen from FIGS.1-7 that a preferable width and length of the burner 16 are at leasthalf of the width and length of the interior of the upper portion ofcombustion chamber 6, other dimensions are also acceptable.

The combustion air inlet 18, such as a venturi inlet, of burner 16supplies virtually all of the combustion air used in generating infraredradiation. In the air inlet 18, air is entrained in the jet stream ofgas emerging through a small orifice. The gas-air mixture flows throughseveral holes, not shown, in the ceramic front of the burner. It burnsclose to the burner surface and heats the surface to a high temperature,up to 1700° F. This then loses heat by radiation, creating the infraredambient.

In FIG. 1, the burner 16 is angled at approximately 8° upward to aidflow of combustion gases away from the burner surface. Radiation exits aradiating surface 3 of the burner 16 in a broad distributed beam through180°.

A metal screen 24 is provided at a distance from the radiating surface22 side of the burner 16 in the combustion chamber 6, and heats up andradiates in all directions, some contributing to heat output, and someadding heat to the burner's radiating surface 3 and thus heating itfurther and intensifying its radiation. In FIG. 1, the metal screen 24is attached to the side wall 8.

The combustion chamber is provided with an outlet passage 26 that allowscombustion product gases to exit the combustion chamber. The outletpassage also draws and pulls air in to cool the sealing barrier 14. Theoutlet passage includes an air-entrainment by turbulence chamber 30, anda vent 32. The outlet passage 26 is preferably positioned in the topwall (not shown) of the combustion chamber 6 and may extend through theceiling 4 to the space provided below a vent cap 34. The turbulencechamber 30 is preferably rectangular, although other shapes may be used,and preferably extends approximately the width of the heater 2. Thevent, for example, a round pipe 4″ in diameter, extends from the topside of the turbulence chamber 30 to the space provided below the ventcap 34. The vent cap 34 prevents rain and dirt from entering the heaterand keeps the pressure in the two pipes substantially the same in allconditions of wind and weather.

One or more reflectors 36 are provided in the combustion chamber. Forexample, in FIG. 1, a reflector is provided on the inside surface ofeach of the side walls 8, 10 of the combustion chamber 6. The reflectors36 direct the lateral infrared output toward the heated area 38.

The heater 2 includes a cooling air passage 44 for supplying cooling air48 to the combustion chamber 6 and a separate combustion air passage 46for supplying combustion air 50 to the burner 16. In FIG. 1, the coolingair 48 is separated from the combustion air 50 for sufficient distanceto prevent admixture of the two. This allows segregation of incomingcombustion air 50 from the combustion chamber 6 so that combustionproducts are not recirculated.

The cooling air passage 44 is located within the heater 2 and adjacentto the combustion chamber 6 and shares a common wall with the side wall10 and communicates with the combustion chamber 6 through a slot 52,which is preferably provided adjacent to the inner upper surface of thesealing barrier 14. If the heater 2 is to be operated at an angleinstead of flat, the slot 52 should be in the upper side wall 10.Because the cooling air 48 that is provided to the combustion chamber 6through the slot 52 is cooler than air within the combustion chamber 6,the cooling air 48 flows down along the inner surface of the sealingbarrier 14 to keep it below the melting point.

In FIG. 1, for example, the source of the cooling air 48 is outside thespace to be heated 38 (e.g., another room, outside environment, etc.)Also, the width of the slot 52 may approach up to the full width of thecombustion chamber 6. The purpose of the slot 52, for example, is todirect cooling air from the cooling air passage 44 into the combustionchamber 6 in the vicinity of the inner surface of the sealing barrier 14to form a constantly replenished pool of cooling air 48 above thesealing barrier 14 to cool the same.

In FIG. 1, a sensor 54 (e.g., temperature sensing device) is provided inthe combustion chamber to detect hot combustion products, for example,in the event of disruption of the sealing barrier 14. The sensor 54 maybe provided near the bottom of the inside top surface of the combustionchamber 6, for example, in order to sense abnormal circulation. Thesensor 54 may comprise a switch with a thermocouple or the like to opena safety circuit before hot products reach the front of the combustionchamber 6. The sensor 54 may also be a nylon line (which has a meltingpoint well below Teflon) that holds closed a switch in the safetycircuit. Other types of known sensors may also be used.

In FIG. 1, the combustion air passage 46 is located within the heater 2and adjacent to the combustion chamber and shares a common wall withside wall 8 and communicates with the burner 16 through the combustionair inlet 18. Here, the combustion air 50 is drawn through thecombustion air passage 46 by the gas jet's entrainment effect. Thecombustion air 50 becomes warm, which improves combustion efficiency.The combustion air also prevents the top of the heater 2 from becomingoverheated so that the heater 2 can be hung on or close to a ceiling orwall, for example, without risking damage thereto. In FIG. 1, forexample, the source of the combustion air 50 is outside the space to beheated 38.

It is also possible for combustion air 50 and cooling air 48 to flowtogether through the vent 32. However, before there is a chance ofadmixture with combustion products, the mixed-function passage dividesinto two separate passages 44, 46.

In FIG. 1, a deflector screen 56 is provided as a barrier on the outsideof the sealing barrier 14 to protect the sealing barrier 14. Thedeflector screen 56 may comprise reflective material, such as aluminum.

FIG. 2 is an alternative embodiment of the present invention and likereference numerals denote similar elements described above. In theheater embodiment of FIG. 2, the burner 16 (e.g., infrared generator) ismounted vertically in the combustion chamber 6 and side wall 10 of thecombustion chamber 6 slants downwardly adjacent a burner base 58 andbeneath the burner 16 at an angle of, e.g., 45° to the horizontal, andis provided with an infrared reflective inner surface 36. The sealingbarrier 14 extends from side wall 10 to side wall 8, at an angle of,e.g., 45°-75° to the horizontal.

Gas enters through the burner base 58 from a controlled source ofsupply, which is not shown. The gas jets through a small orifice 60 andentrains the primary air required for combustion. The gas-air mixturepenetrates numerous openings, not shown, in the front surface of theburner 16 which is usually ceramic or heat-tolerant steel. When thegas-air mixture burns at this surface it heats the surface to very hightemperatures and causes it to give off radiant heat. The combustionproducts that form at the burner surface rise and exit through the vent32. Combustion products exit through the upper portion of the compoundvent cap 34, which keeps the hot products emerging from the ventsegregated from the air going into the cooling air passage 44 andcombustion air passage 46. This arrangement allows the ambientatmospheric pressure in the vent 32 and in the air intakes 44, 46 toessentially be identical (e.g., improves efficiency of heater andnegates wind-generated pressure changes and their effects.)

Combustion air 50 is drawn through a segregated combustion air passage46 by the gas jet's entrainment effect. As shown in FIG. 2, thecombustion air 50 passes along the back of the burner 16, this has atleast the following desirable effects: It becomes somewhat warm, whichimproves combustion efficiency, and it keeps the back of the heater 2from becoming overheated.

Cooling air 48 is drawn through a segregated cooling air passage 44 bythe suction created by ascending combustion products in the vent 32(e.g., draw created in a well-designed fireplace.) It enters thecombustion chamber through a cooling air slot 52 provided, for example,adjacent to the inner upper surface of the sealing barrier 14. Beingcooler than air within the combustion chamber, the cooling air flowsdown along the inner surface of the sealing barrier 14 and keeps it wellbelow its melting point.

FIG. 3 is an alternative embodiment of the present invention and likereference numerals denote similar elements described above. In theheater embodiment of FIG. 3, a partition 62, provided in the heater 2and extending in a generally vertical direction, segregates thecombustion air passage 46 from the cooling air passage 44. As shown inFIG. 3, the bottom wall of the cooling air chamber 48 and the combustionair chamber 50 is the downwardly sloping (e.g., 15°-75° from sealingbarrier 14) side wall 8 of the combustion chamber 6. The side wall 8extends the full width of the heater 2.

A cooling air slot 52 is preferably provided in the side wall 8 toconvey cooling air into the combustion chamber 6 adjacent to the sealingbarrier 14. If the burner 16 is operated off the horizontal (e.g., 20°),then the slot 52 should be preferably provided at the raised side ofside wall 8 in order to better allow cool air to sweep across thesealing barrier 14 by convection.

As shown in FIG. 3, a conduit 64 (e.g., a pipe or duct, etc.) connectsthe turbulence chamber 30, which communicates with the combustionchamber 6 and is provided above the burner 16, with the vent 32. Theconduit 64 penetrates, e.g., the upper portion, the side wall 8 of thecombustion chamber 6 in a sealed manner.

Although not shown in the drawings, a bottom wall should be provided onthe turbulence chamber 30, if the burner 16 does not seal it off fromthe combustion chamber 6.

Combustion air 50 is provided into the burner 16 via an inlet 18 (e.g.,venturi inlet) that is provided in the combustion air passage 46.

Side wall 10 of the combustion chamber 6 is downwardly sloping (e.g.,15°-75° from sealing barrier 14). A reflector 36 is provided on theinside surface of the side wall 10 and directs infrared generated by theburner 16 downward and out through the sealing barrier 14.

A second window 66 (e.g., preferably made of Teflon) is providedadjacent the sealing barrier 14 and away from the heater 2. Window 66may be located in the outside wall of a structure to be heated. Heater 2can be then located entirely outside the structure with the beam ofinfrared it generates largely penetrating window 66 to provide heatinside the structure. The small amount of infrared absorbed in thethermoplastic film of window 66 heats it only slightly, and that heat isdissipated by convection into the surrounding outdoor air to keep thefilm well below its melting point. Sufficient space 80 should generallybe allowed between heater 6 and window 66 to permit convection-generatedcooling to occur.

Having the vent 64, the combustion air passage 44 and the cooling airpassage adjacent to each other eliminates any effects of wind-generatedpressure changes and prevents any conditions of wind or weather fromcreating back drafts. Locating the heater 6 in outdoor space rather thaninside the structure to be heated eliminates hazards related to indoorheating, such as carbon monoxide poisoning and gas leakage.

FIG. 4 is an alternative embodiment showing a second window 66 installedon an upper, center portion of a tent 68. However, the second window 66may also be installed in work shacks, ice fishing houses, huntingshacks, campers, etc., so that the heater can be used in multiplelocations.

The tent 68 includes a tent frame 70 (e.g., four or six legs), straps 81(e.g., Velcro, snap, etc.) provided at various locations to fasten thetent 68 to the frame 70, a heater 2 (e.g., FIG. 2) having an air-cooledsealing barrier 14, and a second window 66 installed on an upper, centerportion of a tent. The circumference of the second window is larger thanthat of the sealing barrier 14 so that tent material at its edges is notheated by the excessive infrared ambient. The second window 66 istransparent to infrared. The heater 2 is entirely separate from, but issupported by a part of the tent frame 70 above the second window 66 sothat it radiates heat into the tent 68.

The heater 2 may be attached to a stand (e.g., 10′ tall) and used, forexample, as an overhead patio heater.

FIG. 5 is an alternative embodiment of the present invention and likereference numerals denote similar elements described above. The heater 2shown in FIG. 5 includes a vent 32, side walls 8, 10 that are providedwith multiple cooling air slots 52 to admit drawn-in cooling air 48, asealing barrier 14, a combustion air passage 46 providing combustion air50 to a burner 16 that is mounted vertically in the combustion chamber6.

In outdoor locations, the pressure at cooling air slots 52 and vent 32is substantially similar and change similarly with the wind.Accordingly, air within the heater 2 moves only in response to heatproduced convection.

This allows use of much more efficient infrared-producing burners thanthe steel-can-heated-from-inside currently used in most outdoor heaters.The more efficient burners have flame which burns in the surface ofceramic or woven-steel. The pressure differential that brings thegas-air mixture through the plurality of holes in the ceramic or steelto its surface is small. For example, it is produced by gas atrelatively low pressure (11-12 inches water column for LP, 4 inches fornatural gas) flowing through a small orifice. This both entrains air anddrives the gas-air mixture to the radiating surface. Thus, the moreefficient type of burner requires wind-pressure control like thatprovided in this heater, because a slight breeze drives the flame backinto or away from the ceramic or steel and drops efficiency.

FIG. 6A is an alternative embodiment of the present invention and likereference numerals denote similar elements described above. The body ofthe heater 2 shown in FIG. 6A is of a cylindrical shape, for example,and includes an outer wall made up of a cylinder 74 (e.g., 6″ pipe), abase 76, and a sealing barrier 14 (preferably, Teflon) provided betweenthe cylinder 74 and the base 76. The sealing barrier is attached to thecylinder 74 and the base 76, for example, by a plurality of fixtures 78(e.g., hose clamps, etc.) Cooling air and combustion air are drawntogether from a compound vent (not shown) into combined passage 82. Apassage for combustion air with top and bottom walls shown as 83 andside walls not shown, which define a passage 85 from the common passage82 without obstructing the vent 84. Teflon cooling air continues pastthe openings to combustion air passage to cooling air passage 44 andthence to flow cooling air 48 down along the inner side of the radiationtransmissive panel. This cool air moves downward rapidly whilecombustion products move upward rapidly creating a shear plane whichprevents combustion product heat form reaching the radiationtransmissive panel.

A cooling air chamber 44, provided generally vertical to the base 66 andadjacent to the sealing barrier 14, draws cooling air 48 to the sealingbarrier 14 and the base 66. The heater includes a tall cylindricalburner 16 that is located approximately in the center of the heater 2and extends in a downward, vertical direction towards the base 76.

FIG. 6B is a cross-sectional view taken along lines 6B-6B of FIG. 6A.

FIG. 7 is an alternative embodiment of the present invention and likereference numerals denote similar elements described above. In heater 2shown in FIG. 7, for example, cooling air 48 sweeps along the innersurface of the sealing barrier 14 by convection. This enablesconsiderable turbulence in the combustion chamber 6, so that all the airin the combustion chamber 6 contains some carbon dioxide. Therefore, toprevent combustion chamber 6 air from being used as combustion air 50,combustion air 50 is provided from a completely separate source, e.g.,combustion air passage 46.

Vertical rise of combustion products (e.g., through a vent 32) isnecessary to draw cooling air 48 in the cooling air passage 44 to coolthe sealing barrier 14. In FIG. 7, for example, the vent 32 is providedoutside the room to be heated 38. For example, an 8″ length of 3″ pipemay be used. The design structure shown in FIG. 7 allows the heater 2 tobe more compact.

In this detailed description of the preferred embodiments, reference ismade to the accompanying drawings, which form a part hereof, and withinwhich are shown by way of illustration specific embodiments by which theinvention is practiced. It is to be understood that other embodimentsmay be utilized and structural changes may be made without departingfrom the scope of the invention.

1. A gas fired, infrared heating apparatus, comprising: a burner; a combustion chamber; a cooling air passage for supplying cooling air to the combustion chamber; a combustion air passage for supplying combustion air to the burner; and an outlet passage allowing combustion product gases to exit the combustion chamber, wherein the cooling air passage is separate from the combustion air passage.
 2. A heating apparatus of claim 1, wherein said cooling air passage and said combustion air passage derive from the same pressure zone into which the outlet passage empties.
 3. The heating apparatus of claim 1, wherein the combustion chamber further comprises a lower wall providing a generally downwardly open port closed by a sealing barrier that is over 80% transmissive of infrared radiation and prevents gaseous interchange between the combustion chamber and a heated space.
 4. The heating apparatus of claim 3, wherein said sealing barrier is made of a material which melts below 1000° F.
 5. The heating apparatus of claim 3, wherein said sealing barrier is made of Teflon.
 6. The heating apparatus of claim 3, wherein the cooling air enters the combustion chamber through an opening in the cooling air passage adjacent to an inner upper surface of the sealing barrier.
 7. The heating apparatus of claim 1, further comprising a compound vent cap provided above an upper side of the outlet port, wherein said compound vent cap draws outside air for the cooling air passage and the combustion air passage without allowing any admixture of outgoing combustion products with incoming air.
 8. The heating apparatus of claim 1, wherein the outlet passage extends in a vertical direction from the burner.
 9. The heating apparatus of claim 1, wherein the combustion air enters into a burner venturi.
 10. The heating apparatus of claim 1, wherein the combustion air passage is located along the back of the burner.
 11. The heating apparatus of claim 3, wherein an infrared-reflective wire adjacent to an inner surface of the sealing barrier prevents the sealing barrier from displacing inward.
 12. The heating apparatus of claim 3, further comprising a heat sensor device positioned within the combustion chamber and positioned above the sealing barrier, wherein the heat sensor device is capable of cutting off a gas supply to the burner.
 13. The heating apparatus, according to claim 1, wherein said heating apparatus is provided outside of a structure to be heated, whereby said heating apparatus projects an infrared ambient through an infrared transmissive window into said structure.
 14. A gas-fired heating apparatus, comprising: a burner; a combustion chamber; an outlet passage allowing combustion gases to exit the combustion chamber; means for supplying combustion air from the same pressure zone to which combustion products exit from the burner; means for preventing said entering combustion air from mixing with gases in the combustion chamber; and means for segregating combustion air from cooling air prior to entry into the combustion chamber.
 15. A heating apparatus, according to claim 14, wherein said supplying means is a combustion air passage.
 16. A heating apparatus, according to claim 14, wherein said cooling air is supplied to the combustion chamber in a cooling air passage, from the same pressure zone to which combustion products exit from the burner.
 17. A heating apparatus, according to claim 14, wherein said outlet passage is provided outside a room to be heated so that said heating apparatus is more compact.
 18. The heating apparatus, according to claim 14, wherein said heating apparatus is provided outside of a structure to be heated, whereby said heating apparatus projects an infrared ambient through an infrared transmissive window into said structure. 